Project Summary/Abstract PEG 3350 is polymeric medicine that is commonly used to treat constipation and for colon cleansing prior to colonoscopy. Although PEG 3350 is only approved by the U.S. FDA for use in people ?17 years of age for no more than seven days, this medicine is very commonly used in young children, often at adult doses, for months or years at a time. The safety of PEG 3350 use by children or for prolonged periods is not known. Furthermore, although PEG 3350 is a polymer that is poorly absorbed, batches of this medicine tested by the FDA have been found to contain small amounts of low molecular weight compounds (e.g. ethylene glycol and diethylene glycol) that might be absorbed and are known to be toxic in high enough doses. Finally, some families who have given PEG 3350 to their children have reported symptoms to the FDA that they are concerned may have been caused by PEG 3350 ingestion. In particular, there is a concern that PEG 3350 components might cause neurobehavioral symptoms. To address the potential toxicity of PEG 3350 in children (in response RFA-FD-14-088) we plan to develop exceptionally sensitive assays for PEG 3350 components and metabolites thought to be potentially toxic, enroll children, collect biospecimens, collect detailed linked clinical and behavioral data, and analyze serum specimens. Specifically, we will collect serum from children who take PEG 3350 to treat constipation, but who do not have underlying bowel problems or neurobehavioral problems. We will also collect serum from children who have bowel problems that might predispose to increased PEG 3350 component absorption or who have underlying neurological or neurobehavioral problems that might make them more sensitive to PEG 3350 components. We will also collect neurobehavioral data and clinical history for each child, and stool and urine from a subset of children. In addition, we will enroll children who are not taking PEG 3350 in case unexpected metabolites are detected in biospecimens from children who are taking PEG 3350. Sample analysis will be performed using state-of-the-art equipment in the Metabolic Disease Laboratory at our institution, the Children?s Hospital of Philadelphia. As a large pediatric gastroenterology group we have recommended PEG 3350 to many children since this medicine was first approved by the FDA for adult use and we are very interested in working with the FDA to assess the safety of this medicine in children.